Answer:
d) have
Explanation:
Ok so the reason for the answer being D) is because if you take answer choice A) and put it in the blank spot and read the sentence you get "I have been not seen him since long" which doesn't sound right. The answer choice B) would be "I am not seen him since long" which also doesn't sound right. Answer choice C) would then be "I had been not seen him since long" which once again doesn't sound right. Now finally if you take answer choice D) and put it in the blank spot you get "I have not seen him since long" which sounds way better than the rest of the answer choices. That is how I got the answer D)
